FIG. 1 shows a wheel W transitioning a gap G and a rise R between a first surface S1 and a second surface S2. As the terms are used herein, a gap refers to a lateral spacing between surfaces and a rise refers to a height transition between surfaces. The wheel W has a wheel diameter D. When transitioning the gap G and the rise R between the surfaces S1 and S2, the wheel W sinks within the gap G, thereby increasing the vertical distance over which the wheel W must travel from the rise R to a distance R1.
Increasing the diameter D3 of the wheel W would aid in overcoming the gap G and the rise R. However, practical considerations limit the usefulness of the wheel W as the diameter D increases. For example, increasing the diameter D of the wheel W increases the amount of force necessary to push the wheel W forward. Further, increasing the diameter D of the wheel W also increases the turn radius and rotational inertia of the wheel W, thereby lessening maneuverability. Moreover, some wheel products may be designed to fit a particular wheel size or range of wheel sizes. Increasing the diameter of the wheel may require a redesign for the product.
One example environment in which a wheel may need to travel over such a surface transition is a train platform. A baggage cart, suitcase, or other wheeled object may need to travel between a platform and a train. Typically, a gap exists between the platform and the floor of the train. In different situations, the floor of the train may be lower than, flush with, or higher than the platform surface. Accordingly, one or more wheels will need to transition over the horizontal and/or vertical distance between the two surfaces.
For a user of a cart that has a caster wheel design with a dual wheel caster, a three inch gap transition on a floor surface—the maximum gap allowed by the ADA—can be a real challenge to traverse. The caster wheels may sink into the gap, especially if the cart is heavily loaded, thereby creating a rise that also needs to be traversed. When a dual wheel caster is presented to a surface having both a gap and a rise, the caster wheels may fall into the gap and the rise to be transitioned includes both the initial surface rise and the fallen distance.
Improvements are desired.